Magnetron



June ro, 1941.

. woLFF 2,244,753 MAGNETRON Filed Ju1y'27, 1939l Fl'grl Mllll'lllu +V(Ittorneg Patented June 10, 1941 VUNlTl-:D STATES PATENT oFFlcEfMAGNETRON Irving Wolff, Merchantville, N. J., assgnor to RadioCorporation of America, acorporation of Delaware Application July 27,1939, Serial No. 286,749

(Cl. Z50-27.5)

7 Claims.

'I'his invention relates to magnetrons and particularly to magnetronshaving means adapted to reduce the velocity of electrons impinging onthe collecting electrodes to thereby increase the eiiciency of thedevice.

The principal object of this invention is to increase the efficiency ofa magnetron oscillator, detector, or ampliiier -by reducing the velocityof electrons which impinge on the end plate or other collectingelectrodes so that the energy loss represented by the heating of thecollecting electrodes is greatly reduced. Further objects of thisinvention include the provision of 'an improved electrode structure forthenmionic discharge tubes of the magnetron type, and the provision ofone or more auxiliary grid electrodes which are located adjacent thecollecting electrode.

This invention will -be better understood from the followingldescription when considered in connecton with the accompanying drawing.Its scope is indicated by the appended claims.

Figure 1 of the drawing represents the application of this invention toa conventional magnetron; and Figure 2 represents the application ofthis invention to a magnetron of the electron beam type.

Referring to Fig. 1 of the drawing, a filamentary cathode I is mountedwithin an evacuated envelope 3 in the usual manner. Surrounding thecathode is a segmented cylindrical oscillatory anode electrodecomprising two semicylindrical sections -5 and I which are connected,respectively, to the two conductors 9 and II of a resonant Lecher wiresystem, which terminates in an antenna. I3. A positive potential issupplied from a battery I5, or the like, which is connected between bothoscillatory electrode segments and the cathode.

A pair of end plate collecting electrodes I'I and I9 are mountedadjacent the opposite ends of the anode structure, and are perpendicularto the axis of the cathode. End plate electrodes, as such, are wellknown in the art. They consist of small metallic discs which areconnected to a source of positive potenti-al. Their purpose is to dra-welectrons from the anode-cathode region to prevent the building up of aspace charge near the cathode. They are mounted within the envelope inany lconvenient manner, las is well known.

An axial magnetic field is produced by means of a magnet, the polepieces of which are indicated at S and N. I have found that the eciencyof operation of a conventional magnetron oscillator having oscillatoryand end plate collecting electrodes is greatly reduced by the energywhich is absorbed in the end plate collecting electrodes. The collectingelectrodes are at a high positive potential so that electrons releasedfrom the cathode are given lan axial velocity which is of such amagnitude that the electrodes frequently become extremely hot. v

For stable operation I have found that the voltage aipplied to the endplates may be suicient to produce an end plate direct current which isas much as fifty times the direct oscillatory electrode current. Thusthe major part of the power dissipation in such a magnetron is in theend plates. Since oscillations are produ-ced between the t'wo segmentsof the cylindrical electrode it is called the `oscillatory electrode,while the end plate electrodes are also known as collecting electrodes.

In accordance with the present invention, a pair of recticular'accelerating electrodes 2I and 23 are located between each end platecollecting electrode and the respective adjacent end of theanodestructu-re. A high positive potential with respect to the cathodeis applied to the accelerating electrodes 2l, 23, lby means of a`suitable tap on the battery I5. The end plate electrodes, however, arelplaced at a lower positive potential with respect to the cathode, bymeans of a separate battery or a connection to battery I5, or the like.The amplitude of the positive potential on the accelerating electrodesis adjusted so that the desired axial Velocity is given to electronswhich are released from the cathode. but due to the grid-like structureof the accelerating electrodes, most of the electrons ypass through theaccelerating electrodes at a high velocitywand come within the influenceof the less positive end plate collecting electrodes I'I and I9. Asaresult,y their velocity is greatly reduced so that when they impinge onthe end plate electrodes, they -contain little or no energy.

When accelerating grids are used the end plate collecting electrodesfunction as decelerating electrodes. The .amplitude of the potentialwhich is applied to the decelerating end plate electrodes must be madehigh enough so that the desired electron flow can be obtained, takinginto account space :charge effects in the space between the acceleratingand the decelcrating electrodes. The decelerating electrode is designedto minimize these eiects. The potential of the accelerating electrodei-s adjusted to control the space charge inside the oscillatoryelectrode.

The grid-like accelerating'electrodes 2| and 23 are formed of a numberof parallel wires, or may consist of a grid-like mesh, or may take theform of any of the well known grid electrodes which are common in theprior art.

While I have illustrated a magnetron utilizing a pair of-semiicylindrical anode electrodes, it is to be understood that thisinvention is not limited to the particular arrangement shown. Forexample, Fig. 2 illustrates the application of this invention to .amagnetron of the electron beam type, a description of which is foundcommencing at page 14 of a book entitled Magnetron-Oscillations ofUltra-short Wavelengths and Electron- Oscillations in General -byKinjiro Okabe, published in Japan by Shokando.

The structural arrangement of an electron beam magnetron comprises acylindrical electrode 25 at one end of which a ycathode 21 is mounted.Facing the open end of cylinder 25 opposite the cathode are twosemicircular anode or oscillatory electrodes 29 and 3|, to which Iaresonant Lecher wiresystem 33 and an antenna 35 are connected. An aXi-almagnetic i-leld is provided by a eld winding 39. The previously knownarrangements, however, do not include the spiral grid 3l which ismounted within the cylindrical electrode 25.

Neglecting for a moment the function of the grid, the operation of thetube is believed to be as follows: Electrons released from the cathode21 are directed radially outwards by the positive potential of cylinder25, which then functions as an accelerating electrode. The magneticfield, however, causes the electrons to rotate about the axis of thecylinder, while the positive potential applied to the anode electrodes29, 3! causes them to move axially away from the cathode. By properlyrelating the resonant period of the oscillatory circuitl 33 with theperiod of revolution, oscillations are sustained in the oscillatorysystem 33.

In accordance with this invention a grid accelerating electrode 31 isplaced between the cathode 21 and the collecting electrode 25. rlhecylindrical electrode 25 then becomes the decelerating electrode and thegrid 3l is the accelerating electrode. The purpose and operation of thegrid is the same as in the previous illustration, and need not beexplained again in detail.

I claim as my invention:

1. An electron discharge device comprising cathode and anode electrodesmounted within an evacuated envelope, a. pair of accelerating electrodesrespectively positioned adjacent the opposite ends of said anodeelectrode, and a pair of decelerating end plate electrodes adjacent saidaccelerating electrodes.

2. A magnetron comprising a linear cathode, a cylindrical electrodemounted about said cathode,

a pair of reticular accelerating electrodes respectively positionedadjacent the opposite ends of said cylindrical electrode andperpendicular to said cathode electrode, and a pair of decelerating endplate electrodes, said accelerating electrodes being positioned betweensaid cylindrical and said decelerating end plate electrodes.

3. An electron discharge device comprising a cathode, a, cylindricalelectrode positioned about said cathode, a pair of acceleratingelectrodes respectively positioned adjacent the opposite ends of saidcylindrical electrode, and a pair of decelerating end plate electrodesexternal to Said accelerating electrodes, said accelerating electrodescomprising a grid-like mesh positioned between said cylindrical and saiddecelerating electrodes and adapted to attract electrons liberated b-ysaid cathode.

4. The combination including an electron emit- .ting cathode, anoscillatory electrode positioned about said cathode, means for causingelectrons emitted from said cathode to follow spiral paths about saidcathode, accelerating electrodes positioned opposite the open ends ofsaid oscillatory electrode for causing portions of said electrons tomove in axial directions parallel to said cathode, and electrode meansfor establishing a decelerating potential gradient for reducing theaxial velocity of said electrons.

5. The combination within an evacuated envelopeof an electron emittingcathode, an oscillatory electrode,l means for causing electrons emittedfrom said cathode to follow spiral paths about an axis passing throughsaid cathode, collecting electrodes, and means including a reticularaccelerating electrode positioned in the path of said electrons forcausing a portion of said electrons to impinge on saidcollectingelectrodes.

6. The combination including an electron emitting cathode, a segmentedcylindrical anode positioned about said cathode, means for causingelectrons emitted from said cathode to follow spiral paths about saidcathode, end plate electrodes positioned opposite the open ends of saidanode and lying in planes perpendicular to said cathode ior collectingelectrons which impinge thereon, and electrode means for reducing thevelocity of said impinging electrons.

7. An electron discharge device comprising a lamentary cathode, asegmented cylindrical anode disposed about said cathode, a pair ofgrid-likeV accelerating electrodes disposed, respectively, adjacent theopposite ends of said anode and lying in planes perpendicular to Vsaidcathode, and a pair of decelerating end plate electrodes adjacentrespective accelerating electrodes and parallel thereto. Y

IRVING WOLFF.

